The invention is based on a fuel injection pump for internal combustion engines. In a fuel injection pump known from German Offenlegungsschrift No. 32 13 724, the pump piston has as its relief conduit an axial blind bore originating at the pump work chamber, from which bore a transverse conduit branches off to two first outlet openings, and a radial conduit also branches off to a second outlet opening. This outlet opening is offset with respect to the first outlet openings toward the pump drive side and cooperates with a radial bore, which is disposed in the annular slide and by way of which the communication with the relief chamber can be established. In the known fuel injection pump the radial bore is disposed such that, at an annular slide position corresponding to the low-load operating range during the pump piston supply stroke, the second outlet opening is in communication with the radial bore, while in the full-load range, the second outlet opening does not come to communicate with the radial bore. This apparatus serves to allow only some of the supply strokes of the pump piston to be effective in the low-load range; accordingly, a plurality of radial bores are provided, distributed around the annular slide, so that only every other pump piston supply stroke, for instance, leads to a pressure buildup in the pump work chamber and hence to the injection of fuel. Correspondingly, only half of the cylinders of the internal combustion engine serve to drive the engine. This provision is meant to lower fuel consumption in the partial-load range.
A fuel injection pump is also known from German Offenlegungsschrift No. 32 18 275, in which instead of the radial bores in the annular slide provided in the above-described known fuel injection pump, diametrically extending grooves originating at the end face of the annular slide are provided, which now cooperate with only a single outlet opening of the relief conduit. The annular slide here is not only axially displaceable on the pump piston as a function of the adjustment of a fuel injection quantity regulator, but is also rotatable by a torque device. By means of rotation, during the supply stroke of the pump piston, the outlet opening can be made to come into communication with one of the diametrically extending grooves in alternation, upon every supply stroke, or every other supply stroke, of the pump piston, depending on the number of grooves provided. Thus, either the number of injections can be reduced by half, for example, similarly to what is known from the prior art described initially above, or the high-pressure supply of the fuel injection pump can be suppressed entirely. Furthermore, by reducing the width of the grooves, it is possible merely to throttle the outflow or "leakage" of fuel during a particular supply stroke, which is intended to function so as to reduce the fuel injection rate in the lower rpm range. This has the effect that the engine can be operated during idling, for example, with reduced combustion noise.
In this known fuel injection pump, problems arise, however, in terms of controlling the quantity of fuel flowing out via the throttle cross sections. In particular, it is problematic to increase the fuel quantity continuously from the transition out of the idling range to the partial-load range, to prevent a load jump upon load take-up. In particular, the outflow of the fuel quantity is dependent, in the known apparatus, on the rpm; that is, it decreases with increasing rpm, because here the throttling action increases together with the decreasing time in throttle cross section. Problems also arise if the fuel injection pump has an associated injection onset adjusting device, which typically means that the first outlet opening is adjusted relative to the drive shaft rotational position of the fuel injection pump.